Optical communication apparatus, optical communication information decoding method, optical switching system, and driving method for optical switching system

ABSTRACT

An optical switching system is disclosed which can achieve high speed optical switching with a simple configuration. Light from a light irradiation section is irradiated into an optical transmission line made of a material having a nonlinear optical effect and disposed on the upstream side with respect to an optical switch provided for performing switching of a transmission line to cause the nonlinear optical effect to occur. Thereupon, light is emitted externally from the optical transmission line by the nonlinear optical effect between the light irradiated by the light irradiation section and light propagating in the optical transmission line. The light emitted is received by a light reception section to acquire intensity information of the light propagating in the optical transmission line. The intensity information is used as driving signal for driving the optical switch.

BACKGROUND OF THE INVENTION

This invention relates to an optical communication apparatus, an opticalcommunication information decoding method, an optical switching systemand a driving method for an optical switching system, and moreparticularly to an optical communication apparatus, an opticalcommunication information decoding method, an optical switching systemand a driving method for an optical switching system suitable for usefor a switching process of multiplexed optical signals.

The field of optical communication has been developing rapidly togetherwith the progress of the information-based society in recent years. Inthe field of optical communication, the progress is significant in thefield of the enhancement in function beginning with the enhancement intransfer rate and the multiplexing of data.

As a multiplexing technique, wavelength multiplexing techniques such asthe WDM (Wavelength Division Multiplexing) and the DWDM (DenseWavelength Division Multiplexing) have been developed.

In such a situation as described above, also with regard to a switchingtechnique required for a repeating point of an optical fibertransmission line (hereinafter referred to merely as optical fiber),specifications for higher performances such as higher speed operation ofan optical switch are demanded.

More particularly, it is demanded to raise the speed of an opticalswitch which quickly decodes header information included in informationpropagating in an optical fiber, that is, information in which adestination of information is recorded, and operates rapidly in responseto the header information.

However, in an environment of the WDM or the DWDM, informationpropagating in an optical fiber and including header information cannotbe read before optical wavelengths are demultiplexed from one another.Therefore, an optical switching system at a repeating point of anoptical fiber cannot be avoided to have such a configuration as shown inFIG. 1.

FIG. 1 shows an optical switching system which distributes and outputswavelength-multiplexed optical signals inputted from an optical fiber 51to optical fibers 52 and 53 in accordance with header information of thewavelength-multiplexed optical signals.

Referring to FIG. 1, wavelength-multiplexed light transmitted along theoptical fiber 51 in accordance with the WDM or DWDM system isdemultiplexed for individual wavelengths by a demultiplexer 54 andindividually received by light reception units 55 a to 55 f. Informationreading apparatus 56 a to 56 f read header information of informationsignals in the form of optical signals of the different wavelengthsreceived by the light reception units 55 a to 55 f, respectively.

The information reading apparatus 56 a to 56 f discriminate destinationsof the individual information signals based on the header information toselect output destinations of the information signals and signal theinformation signals to light emitting elements 57 a to 57 f or lightemitting elements 58 a to 58 f.

For example, if the information reading apparatus 56 a discriminatesthat the output destination of the pertaining information signal is theoptical fiber 52 side, then it outputs the information signal to thelight emitting element 57 a. On the other hand, if the informationreading apparatus 56 a discriminates that the information signal is theoptical fiber 53 side, then it outputs the information signal to thelight emitting element 58 a.

When each of the light emitting elements 57 a to 57 f and the lightemitting elements 58 a to 58 f receives an information signal, it emitslight of an optical signal of a predetermined wavelength correspondingto the information signal.

Optical signals of different wavelengths outputted from all or some ofthe light emitting elements 57 a to 57 f are multiplexed in accordancewith the WDM or DWDM system by a multiplexer 59 and signaled to theoptical fiber 52. On the other hand, optical signals of differentwavelengths outputted from all or some of the light emitting elements 58a to 58 f are multiplexed in accordance with the WDM or DWDM system by amultiplexer 60 and signaled to the optical fiber 53.

In this manner, at a repeating point of an optical fiber, ademultiplexer for demultiplexing wavelength-multiplexed light intodifferent wavelengths used in the WDM or DWDM, light receiving elementsfor the individual wavelengths and a number of light emitting sourcesfor the individual wavelengths equal to the number of fiber transmissionlines used for transmission are required. Therefore, the opticalswitching system has a configuration of a great scale.

Further, since the optical switching system is configured such that ituses a procedure including demultiplexing of multiplexed wavelengths,light reception and information reading in order to select transmissiondestinations, it has a limitation to satisfaction of the demand for highspeed optical switching.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and anapparatus which can decode information included in optical signalstransmitted, for example, in accordance with the WDM or DWDM systemwithout demultiplexing the optical signals.

It is another object of the present invention to provide an opticalswitching system and a driving method for an optical switching systemwhich can achieve high speed optical switching with a simpleconfiguration.

In order to attain the objects described above, according to the firstaspect of the present invention, there is provided an opticalcommunication apparatus which includes an optical transmission line madeof a material having a nonlinear optical effect, a light irradiationsection for irradiating light into the optical transmission line tocause the nonlinear optical effect to occur, and a light receptionsection for receiving light emitted externally from the opticaltransmission line by the nonlinear optical effect between the lightirradiated into the optical transmission line by the light irradiationsection and light propagating in the optical transmission line toacquire intensity information of the light propagating in the opticaltransmission line.

According to the second aspect of the present invention, there isprovided an optical communication information decoding method for anoptical communication apparatus which includes an optical transmissionline made of a material having a nonlinear optical effect, a lightirradiation section for irradiating light into the optical transmissionline to cause the nonlinear optical effect to occur, and a lightreception section for receiving light emitted externally from theoptical transmission line by the nonlinear optical effect of the opticaltransmission line, including the step of receiving the light emittedexternally from the optical transmission line by the nonlinear opticaleffect between the light irradiated into the optical transmission lineby the light irradiation section and light propagating in the opticaltransmission line by means of the light reception section to decodeheader information of the information propagating in the opticaltransmission line.

According to the third aspect of the present invention, there isprovided an optical switching system for switching a transmission linein response to information propagating in an optical transmission linewhich includes an optical switch for performing switching of atransmission line, an optical transmission line made of a materialhaving a nonlinear optical effect and disposed on the upstream side withrespect to the optical switch, a light irradiation section forirradiating light into the optical transmission line to cause thenonlinear optical effect to occur, a light reception section forreceiving light emitted externally from the optical transmission line bythe nonlinear optical effect between the light irradiated into theoptical transmission line by the light irradiation section and lightpropagating in the optical transmission line to acquire intensityinformation of the light propagating in the optical transmission line,and driving means for producing a driving signal for the optical switchfrom the intensity information acquired by the light reception section.

According to the fourth aspect of the present invention, there isprovided a driving method for an optical switching system for switchinga transmission line in response to information propagating in an opticaltransmission line, including the steps of irradiating light from a lightirradiation section into an optical transmission line made of a materialhaving a nonlinear optical effect and disposed on the upstream side withrespect to an optical switch which performs switching of a transmissionline, receiving light emitted externally from the optical transmissionline by the nonlinear optical effect between the light irradiated by thelight irradiation section and light propagating in the opticaltransmission line by means of a light reception section to acquireintensity information of the light propagating in the opticaltransmission line, and producing a driving signal for the optical switchbased on the intensity information.

In the optical communication apparatus, optical communicationinformation decoding method, optical switching system and driving methodfor an optical switching system, the light emitted externally from theoptical transmission line by the nonlinear optical effect may have awavelength different from that of the light propagating in the opticaltransmission line.

Where the light propagating in the optical transmission line has aplurality of wavelengths, the light emitted externally from the opticaltransmission line by the nonlinear optical effect may have a pluralityof wavelengths corresponding to the plurality of wavelengths propagatingin the optical transmission line.

Where the light propagating in the optical transmission line has aplurality of wavelengths, the light emitted externally from the opticaltransmission line by the nonlinear optical effect may be emitted in aplurality of directions corresponding to the plurality of wavelengthspropagating in the optical transmission line.

Preferably, the light irradiated into the optical transmission line bythe light irradiation section to cause the nonlinear optical effect tooccur is a laser beam.

The light irradiation section may include a resonator, in which anoptical transmission line made of a material having a nonlinear opticaleffect is disposed.

With the optical communication apparatus, optical communicationinformation decoding method, optical switching system and driving methodfor an optical switching system, for example, where optical signalsmultiplexed with different wavelengths in accordance with the WDM systemor the DWDM system are transmitted, information included in the opticalsignals can be decoded at a stage before they are demultiplexed fromeach other through the utilization of a nonlinear optical effect in theoptical transmission line, and a switching operation for opticalswitching can be performed in response to the decoded information.Consequently, there is an advantage that a temporal intensity variationof the light propagating in the optical transmission line can be decodedfor each of the wavelengths of the light signals before the light isdemultiplexed.

Further, even in an environment of a system wherein differentwavelengths are involved such as the WDM system or the DWDM system,information of each wavelength, specifically header information, can bedecoded without using a demultiplexer. Therefore, the processing timewhen an optical switch is driven can be reduced.

Furthermore, the optical switching system can be formed in a simplifiedconfiguration because there is no necessity to prepare light emittingelements (light sources) for individually different wavelengths.

The above and other objects, features and advantages of the presentinvention will become apparent from the following description and theappended claims, taken in conjunction with the accompanying drawings inwhich like parts or elements denoted by like reference symbols.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of a conventionaloptical switching system;

FIG. 2 is a schematic view showing a configuration of an opticalcommunication apparatus to which the present invention is applied;

FIGS. 3 and 4 are wave number vector diagrams where a frequencydifference of a parametric oscillation phenomenon is used in the opticalcommunication apparatus of FIG. 2;

FIG. 5 is a schematic view showing a configuration of another opticalcommunication apparatus to which the present invention is applied;

FIG. 6 is a schematic view showing a configuration of an opticalswitching system to which the present invention is applied;

FIG. 7 is a schematic view showing a configuration of a further opticalcommunication apparatus to which the present invention is applied; and

FIGS. 8 and 9 are wave number vector diagrams where a frequencydifference of a parametric oscillation phenomenon is used in the opticalcommunication apparatus of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 2, there is shown an optical communication apparatusto which the present invention is applied. The optical communicationapparatus shown is formed as a repeating apparatus for supplyingpropagation light having communication information and transmittedthereto from an optical fiber 1 to another optical fiber 2.

The propagation light here is light wavelength multiplexed, for example,in accordance with the WDM or DWDM system.

The optical communication apparatus of the first embodiment includes alens 3, a nonlinear optical crystal member 4 in which an opticalwaveguide 5 is formed, another lens 6, a YAG laser lot 7, mirrors 8 and9, and a PD (photo-detector) array 10.

Propagation light having communication information propagates along theoptical waveguide 5 (for example, an optical waveguide element made of alithium niobate material) formed by the nonlinear optical material 4 ina transmission line, more particularly, between the optical fibers 1 and2.

The optical parts (YAG laser lot 7 and the mirrors 8 and 9) forirradiating a high-intensity laser beam from the outside of the opticalwaveguide 5 are arranged for the optical waveguide 5.

The optical parts and the optical waveguide 5 are arranged such that aninteraction between the propagation light having the communicationinformation which propagates in the optical waveguide 5. The laser beamirradiated from the outside of the optical waveguide 5 by the YAG laserlot 7 and the mirrors 8 and 9 occurs such that light having wavelengthsdifferent from those of the propagation light having the communicationinformation which propagates in the optical waveguide 5 is emitted tothe outside of the optical waveguide 5.

The PD array 10 is arranged outside the optical waveguide 5 and includeslight receiving elements (photo-detectors) PD for converting the lightemitted to the outside of the optical waveguide 5 into electric signals.

Here, the interaction between the propagation light having communicationinformation which propagates in the optical waveguide 5 and the laserbeam irradiated from the outside particularly is a phenomenon such asparametric oscillation based on a nonlinear optical constant of thenonlinear optical material 4. As seen in FIG. 3, the interaction is anaction wherein light is emitted with a wavelength and in a directionwhich satisfy a wave number vector Ko1 which depends upon a wave numbervector Kf1 of the light which propagates in the transmission line and awave number vector Kr of the light irradiated from the outside.

It is to be noted that the parametric oscillation phenomenon includestwo phenomena of a frequency difference and a frequency sum. FIG. 3illustrates a relationship of vectors where the phenomenon of thefrequency difference is used.

The parametric oscillation phenomenon is a phenomenon wherein light of awave number vector determined by a wave number vector of light whichpropagates in the transmission line and a wave number vector of lightirradiated from the outside is emitted externally. Therefore, even ifthe light irradiated from the outside has a single frequency, if anotherlight having a different wavelength propagates in the transmission line,then the light is emitted externally with a wavelength and in adirection which satisfy a wave number vector Ko2 which depends upon awave number vector Kf2 of the light which propagates in the transmissionline and a wave number vector Kr of the light irradiated from theoutside as seen from a wave number vector diagram of FIG. 4.Consequently, lights having wavelengths different from each other areemitted externally in directions corresponding to the wavelengths of thelights which propagate in the transmission line.

Further, if the light irradiated from the outside is light fixed intime, then the externally emitted light includes a temporal intensitydistribution corresponding to a temporal intensity variation of thelight propagating in the transmission line.

In particular, temporal intensity variations for the individualwavelengths of the propagation lights which propagate in thetransmission line, that is, signals corresponding to communicationinformation, are inputted to two light receiving elements PD1 and PD2seen in FIG. 4.

Then, even if the lights which propagate in the transmission line areweek, if the light irradiated from the outside has a high intensity andthere is a situation that the light which transmits in the transmissionline is confined in the transmission line, then the light receivingelements PD1 and PD2 can read the optical information.

If the action described above is adapted to the configuration of FIG. 2,then the transmission line shown in FIGS. 3 and 4 corresponds to theoptical waveguide 5, and propagation light having communicationinformation is confined in the optical waveguide 5. Then, a laser beamhaving a high intensity is irradiated from the YAG laser lot 7 upon theoptical waveguide 5. In this instance, the irradiated laser beam doesnot propagate in the optical waveguide 5, and therefore, is notcondensed by the lens 6 and does not propagate to the optical fiber 2.

Accordingly, temporal intensity variations of the individual wavelengthsincluded in the propagation light which propagates in the opticalwaveguide 5, that is, signals corresponding to the individualmultiplexed communication information, are inputted to a plurality oflight receiving elements PD in the PD array 10.

The optical communication apparatus of FIG. 1 can read several kinds ofinformation multiplexed with different wavelengths withoutdemultiplexing the multiplexed information.

A configuration of another optical communication apparatus to which thepresent invention is supplied is shown in FIG. 5. Referring to FIG. 5,the optical communication apparatus has a resonator configurationprovided at a location at which a light irradiation section whichirradiates light upon the optical waveguide 5 is provided, and anoptical transmission line formed from a material having a nonlinearoptical effect is arranged in the resonator.

It is to be noted that the optical communication apparatus of FIG. 5further includes lenses 3 and 6, an optical waveguide 5 and a PD array10 similar to those of the optical communication apparatus describedhereinabove with reference to FIG. 2.

In the optical communication apparatus of FIG. 5, a YAG laser lot 7, anonlinear optical crystal member 11, and mirrors 8 and 12 are providedas components of the light irradiation section which irradiates a laserbeam from the outside upon the optical waveguide 5. The nonlinearoptical crystal 11 arranged for the YAG laser lot 7 functions as asecond harmonic production element.

In particular, in the optical communication apparatus of FIG. 5, thenonlinear optical crystal element 11 which is a second harmonicproduction element is used to reduce the wavelength of the laser beam.If the wavelength of the laser beam is reduced by the reduction of thewavelength just described to convert the laser beam into a laser beam ofa wavelength shorter than, for example, 1.064 microns, that is, of ahigher frequency, a higher conversion efficiency can be achieved.

FIG. 6 shows an optical communication system to which the presentinvention is applied. The optical communication system shown uses theoptical information reading method of the optical communicationapparatus shown in FIG. 2.

Referring to FIG. 6, the optical communication system uses the opticalcommunication apparatus of FIG. 2 and includes an optical switch 22connected to the optical fiber 2 shown in FIG. 2 for distributing lightfrom the optical fiber 2 to an optical fiber 23 and another opticalfiber 24, and an information reading apparatus 21 for supplying aswitching driving signal CSW to the optical switch 22 to drive theoptical switch 22.

It is to be noted that, although a particular configuration of theoptical switch 22 is not shown in FIG. 6, a known optical switch such asan optical switch composed of a demultiplexer, a micro-mirror array anda multiplexer may be used as the optical switch 22.

In the optical communication system shown in FIG. 6, a decodingoperation of optical information is performed at a stage before signallight is introduced into the optical switch 22, that is, at a stagewherein signal light is propagating in the optical waveguide 5 of thenonlinear optical crystal 4 before it is introduced into the opticalfiber 2.

In particular, since, as described hereinabove in connection with theoptical communication apparatus of FIG. 2, intensity information ofoptical signals of different wavelengths which propagate in the opticalwaveguide 5 is inputted individually to the light receiving elements ofthe PD array 10, the information reading apparatus 21 can decode thesignals obtained by the light receiving elements of the PD array 10 toread information of the multiplexed optical signals such as, forexample, header information.

Accordingly, the information reading apparatus 21 can discriminateoutput destinations of the optical signals of the different wavelengthsand produce a driving signal CSW for the optical switch 22 in accordancewith the output destinations.

Since, in the optical switching system having such a configuration asdescribed above, decoding of optical information of optical signals ofsignal light is performed at a stage before the optical signals areinputted to the optical switch 22, the decoding operation of theinformation is performed at an earlier stage when compared with analternative case wherein the optical signals are demultiplexed to readthe optical information after they have propagated in the optical fiber2. Accordingly, driving of the optical switch 22 can be performed at anearlier stage. In other words, higher speed optical switching can beachieved.

Further, in the optical switching system shown in FIG. 6, the necessityfor preparation of a light source for each wavelength is eliminated whencompared with the conventional optical switching system shown in FIG. 1.Therefore, the optical communication system can be formed with a reducedsize and at a reduced cost.

It is to be noted that, while it is described that a frequencydifference of a parametric oscillation phenomenon is used in the opticalcommunication apparatus and the optical switching system according tothe present invention described above, the present invention is notlimited to such optical communication apparatus or optical switchingsystem in which a frequency difference is used as described above.

FIG. 7 shows a further optical communication apparatus to which thepresent invention is applied. Referring to FIG. 7, the opticalcommunication apparatus shown uses a frequency sum of a parametricoscillation phenomenon. The optical communication apparatus includessimilar components to those of the optical communication apparatusdescribed hereinabove with reference to FIGS. 2 and 5. FIGS. 8 and 9illustrate wave number vectors of the optical communication apparatus ofFIG. 7.

Also the optical communication apparatus of FIG. 7 externally emitslight with a wavelength and in a direction which satisfy a wave numbervector Ko1 which depends upon a wave number vector Kf1 of lightpropagating in the transmission line and a wave number vector Kr oflight irradiated from the outside as seen in FIG. 8.

Further, even if the light irradiated from the outside has a singlefrequency, if another light having a different wavelength propagates inthe transmission line, then the light is emitted externally with awavelength and in a direction which satisfy a wave number vector Ko2which depends upon a wave number vector Kf2 of the light whichpropagates in the transmission line and a wave number vector Kr of thelight irradiated from the outside as seen from a wave number vectordiagram of FIG. 8. Consequently, lights having wavelengths differentfrom each other are emitted externally in directions corresponding tothe wavelengths of the lights which propagate in the transmission line.

From FIGS. 8 and 9, it can be recognized that, even where a frequencysum of a parametric oscillation phenomenon is used, by irradiating alaser beam having a single frequency and fixed in time from the outside,a temporal intensity variation for each wavelength propagating in atransmission line can be detected by means of light receiving elementswhich are provided externally to monitor lights emitted externally withwavelengths and in directions different among different wavelengths froman optical waveguide element made of a nonlinear optical material.

Accordingly, also the optical communication apparatus having theconfiguration described above with reference to FIG. 7 can readinformation of individual wavelengths from multiplexed optical signalspropagating in the optical waveguide 5 by means of the light receivingelements PD of the PD array 10. Naturally, the optical communicationapparatus of FIG. 7 can be used to construct such an optical switchingsystem as described hereinabove with reference to FIG. 6.

In the following, examples of the wavelength and the direction ofexternally emitted light with respect to the wavelength and the incidentangle of incident light are described with regard to two cases includinga case wherein a frequency difference of a parametric oscillationphenomenon is used and another case wherein a frequency sum of aparameter oscillation phenomenon is used.

<Where a Frequency Difference is Used>

(1)-1

Wavelength propagating in optical transmission line: 1.550 microns

Wavelength of irradiated light: 1.064 microns

Incident angle: 10 degrees

Wavelength of externally emitted light: 3.08218 microns

Emitting angle: 3.43666 degrees

(1)-2

Wavelength propagating in optical transmission line: 1.552 microns

Wavelength of irradiated light: 1.064 microns

Incident angle: 10 degrees

Wavelength of externally emitted light: 3.07537 microns

Emitting angle: 3.444429 degrees

Position difference corresponding to wavelength difference 2 nm ofpropagating light where light receiving element is disposed at positionspaced rearwardly by 10 mm from optical waveguide element: 369 microns

(2)-1

Wavelength propagating in optical transmission line: 1.550 microns

Wavelength of irradiated light: 0.532 microns

Incident angle: 10 degrees

Wavelength of emitting light: 0.800402 microns

Emitting angle: 6.62774 degrees

(2)-2

Wavelength propagating in optical transmission line: 1.552 microns

Wavelength of irradiated light: 0.532 microns

Incident angle: 10 degrees

Wavelength of emitting light: 0.799888 microns

Emitting angle: 6.63201 degrees

Position difference corresponding to wavelength difference 2 nm ofpropagating light where light receiving element is disposed at positionspaced rearwardly by 10 mm from optical waveguide element: 56 microns

<Where a Frequency Sum is Used>

(3)-1

Wavelength propagating in optical transmission line: 1.550 microns

Wavelength of irradiated light: 1.064 microns

Incident angle: 10 degrees

Wavelength of emitting light: 0.633237 microns

Emitting angle: 16.96416 degrees

(3)-2

Wavelength propagating in optical transmission line: 1.552 microns

Wavelength of irradiated light: 1.064 microns

Incident angle: 10 degrees

Wavelength of externally emitted light: 0.633568 microns

Emitting angle: 16.95501 degrees

Position difference corresponding to wavelength difference 2 nm ofpropagating light where light receiving element is disposed at positionspaced rearwardly by 10 mm from optical waveguide element: 188 microns

(4)-1

Wavelength propagating in optical transmission line: 1.550 microns

Wavelength of irradiated light: 0.532 microns

Incident angle: 10 degrees

Wavelength of externally emitted light: 0.397211 microns

Emitting angle: 13.4486 degrees

(4)-2

Wavelength propagating in optical transmission line: 1.552 microns

Wavelength of irradiated light: 0.532 microns

Incident angle: 10 degrees

Wavelength of externally emitted light: 0.397341 microns

Emitting angle: 13.4441 degrees

Position difference corresponding to wavelength difference 2 nm ofpropagating light where light receiving element is disposed at positionspaced rearwardly by 10 mm from optical waveguide element: 144 microns

According to the accuracy in production of light receiving elements atpresent, it is easy to produce light receiving elements of the size ofapproximately 10 microns. Therefore, from the results of the calculationabove, it can be seen that a sufficient resolution in position forwavelengths propagating in the optical waveguide 5 is obtained. In otherwords, information propagating in the optical waveguide 5 can be readfor each of wavelengths of the light as described hereinabove inconnection with the embodiments of the present invention.

While preferred embodiments of the present invention have been describedusing specific terms, such description is for illustrative purposesonly, and it is to be understood that changes and variations may be madewithout departing from the spirit or scope of the following claims.

1. An optical communication apparatus, comprising: an opticaltransmission line made of a material having a non-linear optical effect;a light irradiation section for irradiating light into said opticaltransmission line, wherein light propagating in said opticaltransmission line is in a first direction and the irradiating light isin a second direction that differs from the first direction and that isat an incident angle to the light propagating in said opticaltransmission line to cause the non-linear optical effect to occur; and alight reception section for receiving light emitted externally from saidoptical transmission line by the non-linear optical effect between thelight irradiated into said optical transmission line by said lightirradiation section and light propagating in said optical transmissionline acquire intensity information of the light propagating in saidoptical transmission line, wherein the light emitted externally fromsaid optical transmission line by the non-linear effect is in a thirddirection that differs from the first direction and that is at anemitting angle to the light propagating in said optical transmissionline, and wherein the light propagating from said optical transmissionline has a plurality of wavelengths, and the light emitted externallyfrom said optical transmission line by the non-linear optical effect hasa plurality of wavelengths corresponding to the plurality of wavelengthspropagating in said optical transmission line.
 2. An opticalcommunication apparatus according to claim 1, wherein the light emittedexternally from said optical transmission line by the non-linear opticaleffect has a wavelength different from that of the light propagating insaid optical transmission line.
 3. An optical communication apparatusaccording to claim 1, wherein the light propagating in said opticaltransmission line has a plurality of wavelengths, and the light emittedexternally from said optical transmission line by the non-linear opticaleffect is emitted in a plurality of directions corresponding to theplurality of wavelengths propagating in said optical transmission line.4. An optical communication apparatus according to claim 1, wherein thelight irradiated into said optical transmission line by said lightirradiation section to cause the non-linear optical effect to occur is alaser beam.
 5. An optical communication apparatus according to claim 1,wherein said light irradiation section includes a resonator in which anoptical transmission line made of a material having a non-linear opticaleffect is disposed.
 6. An optical communication information decodingmethod for an optical communication apparatus which includes an opticaltransmission line made of a material having a non-linear optical effect,a light irradiation section, and a light reception section for receivinglight emitted externally from said optical transmission line by thenon-linear optical effect of said optical transmission line, whichcomprises: irradiating light into said optical transmission line by thelight irradiation section, wherein light propagating in said opticaltrasmission line is in a first direction and the irradiating light is ina second direction that differs from the first direction and that is atan incident angle to the light propagating in said optical transmissionline to cause the non-linear optical effect to occur; and receiving thelight emitted externally from said optical transmission line by thenon-linear optical effect between the light irradiated into said opticaltransmission line by said light irradiation section and the lightpropagating in said optical transmission line by means of said lightreception section to decode header information of the informationpropagating in said optical transmission line, wherein the light emittedexternally from said optical transmission line by the non-linear effectis in a third direction that differs from the first direction and thatis at an emitting angle to the light propagating in said opticaltransmission line, and wherein the light propagating in said opticaltransmission line has a plurality of wavelengths, and the light emittedextrenally from said optical transmission line by the nonlinear opticaleffect has a plurality of wavelengths corresponding to the plurality ofwavelengths propagating in said optical transmission line.
 7. An opticalcommunication information decoding method according to claim 6, whereinthe light emitted externally from said optical transmission line by thenon-linear optical effect has a wavelength different from that of thelight propagating in said optical transmission line.
 8. An opticalcommunication information decoding method according to claim 6, whereinthe light propagating in said optical transmission line has a pluralityof wavelengths, and the light emitted externally from said opticaltransmission line by the non-linear optical effect is emitted in aplurality of directions corresponding to the plurality of wavelengthspropagating in said optical transmission line.
 9. An opticalcommunication information decoding method according to claim 6, whereinthe light irradiated into said optical transmission line by said lightirradiation section to cause the non-linear optical effect to occur is alaser beam.
 10. An optical communication information decoding methodaccording to claim 6, wherein said light irradiation section includes aresonator in which an optical transmission line made of a materialhaving a non-linear optical effect is disposed.
 11. An optical switchingsystem for switching a transmission line in response to informationpropagating in an optical transmission line, comprising: an opticalswitch for performing switching of a transmission line; an opticaltransmission line made of a material having a non-linear optical effectand disposed on the upstream side with respect to said optical switch; alight irradiation section for irradiating light into said opticaltransmission line, wherein light propagating in said opticaltransmission line is in a first direction and the irradiating light isin a second direction that differs from the first direction and that isat an incident angle to the light propagating in said opticaltransmission line to cause the non-linear optical effect to occur; alight reception section for receiving light emitted externally from saidoptical transmission line by the non-linear optical effect between thelight irradiated into said optical transmission line by said lightirradiation section and light propagating in said optical transmissionline to acquire intensity information of the light propagating in saidoptical transmission line, wherein the light emitted externally fromsaid optical transmission line by the non-linear effect is in a thirddirection that differs from the first direction and that is at anemitting angle to the light propagating in said optical transmissionline, and wherein the light propagating in said optical transmissionline has a plurality of wavelengths, and the light emitted externallyfrom said optical transmission line by the non-linear optical effect isemitted in a plurality of directions corresponding to the plurality ofwavelengths propagating in said optical transmission line; and drivingmeans for producing a driving signal for said optical switch from theintensity information acquired by said light reception section.
 12. Anoptical switching system according to claim 11, wherein the lightemitted externally from said optical transmission line by the non-linearoptical effect has a wavelength different from that of the lightpropagating in said optical transmission line.
 13. An optical switchingsystem according to claim 11, wherein the light propagating in saidoptical transmission line has a plurality of wavelengths, and the lightemitted externally from said optical transmission line by the non-linearoptical effect has a plurality of wavelengths corresponding to theplurality of wavelengths propagating in said optical transmission line.14. An optical switching system according to claim 11, wherein the lightirradiated into said optical transmission line by said light irradiationsection to cause the non-linear optical effect to occur is a laser beam.15. An optical switching system according to claim 11, wherein saidlight irradiation section includes a resonator in which an opticaltransmission line made of a material having a non-linear optical effectis disposed.
 16. A driving method for an optical switching system forswitching a transmission line in response to information propagating inan optical transmission line, comprising the steps of: irradiating lightfrom a light irradiation section into an optical transmission line madeof a material having a non-linear optical effect and disposed on theupstream side with respect to an optical switch which performs switchingof a transmission line, wherein light propagating in said opticaltransmission line is in a first direction and the irradiating light isin a secnod direction that differs from the first direction ad that isat an incident angle to the light propagating in said opticaltransmission line to cause non-linear optical effect to ocur; receivinglight emitted externally from said optical transmission line by thenon-linear optical effect between the light irradiated by said lightirradiation section and light propagating in said optical transmissionline by means of a light reception section to acquire intensityinformation of the light propagating in said optical transmission line,wherein the light emitted externally from said optical transmission lineby the non-linear effect is in a third direction that differs from thefirst direction and that is at an emitting angle to the lightpropagating in said optical trnasmission line, and wherein the lightpropagating in said optical transmission line has a plurality ofwavelengths, and the light emitted externally from said opticaltransmission line by the non-linear effect is emitted in a plurality ofdirections corresponding to the plurality of wavelengths propagating insaid transmission line; and producing a driving signal for said opticalswitch based on the intensity information.
 17. A driving method for anoptical switching system according to claim 16, wherein the lightemitted externally from said optical transmission line by the non-linearoptical effect has a wavelength different from that of the lightpropagating in said optical transmission line.
 18. A driving method foran optical switching system according to claim 16, wherein the lightpropagating in said optical transmission line has a plurality ofwavelengths, and the light emitted externally from said opticaltransmission line by the non-linear optical effect has a plurality ofwavelengths corresponding to the plurality of wavelengths propagating insaid optical transmission line.
 19. A driving method for an opticalswitching system according to claim 16, wherein the light irradiatedinto said optical transmission line by said light irradiation section tocause the non-linear optical effect to occur is a laser beam.
 20. Adriving method for an optical switching system according to claim 16,wherein said light irradiation section includes a resonator in which anoptical transmission line made of a material having a non-linear opticaleffect is disposed.